A phenol resin is a material excellent in the balance between heat resistance, dynamical performance and electric characteristics and the cost, and utilized in various industrial fields. In particular, applicability to various fields has recently been found as to a granular or powdery phenol resin or a hardened substance thereof, and some products are already put on the market as multiuse materials.
For example, Japanese Patent Laying-Open No. 57-177011 (Patent Document 1) discloses a granular or powdery phenol resin hardened substance consisting of a condensate of a phenolic compound and formaldehyde, and this is put on the market with a trade name “Bellpearl (registered trademark) Type R” (by Air Water Inc.). This phenol resin hardened substance is useful as an organic filler for supplying heat resistance or improving sliding properties or a filler for reducing the quantity of gas generated when hardening an unhardened phenol resin or the like, for example. Further, this is a resin having a high residual carbon ratio due to the chemical structure thereof, and hence the same is useful also as a firing precursor of activated carbon or a powdery carbon material suitably used as a carbon electrode material, for example. In addition, the granular or powdery phenol resin hardened substance described in Patent Document 1 contains neither a harmful phenol monomer nor a low-molecular condensation component, and has high safety.
When employing the aforementioned phenol resin powder or the hardened substance thereof as an organic filler or a precursor of a powdery carbon material, the shapes and configrations of the particles thereof must be properly controlled, in order to exhibit desirable performance as the organic filler or the precursor of a powdery carbon material. In other words, it is necessary that (i) the average particle diameter of the particles is sufficiently small, and (ii) there is hardly any secondary aggregate resulting from aggregation of primary particles, in order to attain a high filling property in a product, a high specific surface area in formation of the powdery carbon material and low viscosity in a use as an aqueous slurry. In addition to the above (i) and (ii), it is more desirable that (iii) the particle size distribution of the particles is sufficiently narrow, and/or (iv) the shapes of the particles are closer to a spherical shape. Further, it is desirable that (v) the residue of a phenol monomer (free phenol) in the phenol resin powder is smaller, in consideration of safety of the product to which this phenol resin powder is applied or safety in production. The aforementioned sufficiently small particle diameter must be at least not more than 20 μm, more preferably not more than 10 μm, in consideration of application of the phenol resin powder or the hardened substance thereof to various industrial uses.
However, although a large number of studies have been heretofore conducted as to the phenol resin powder or the hardened substance thereof, it is the present situation that a phenol resin powder having the aforementioned characteristics or a hardened substance thereof is not yet known and a production method suitable for mass production of such a phenol resin powder or a hardened substance thereof is not yet known either.
For example, while the aforementioned Patent Document 1 describes a technique of obtaining a granular or powdery non-thermofusible phenol resin by optimizing synthetic conditions such as the ratios of quantities of formaldehyde, phenol, hydrochloric acid and a water medium as used and a temperature condition, the obtained non-thermofusible phenol resin had such points to he improved that (i) the primary particle diameters are relatively large, (ii) the quantity of secondary aggregates formed by aggregation of the primary particles is relatively large, (iii) the particle size distribution is wide, and (iv) the resin contains a large quantity of particles having shapes other than a spherical shape.
Japanese Patent Laying-Open No. 2000-239335 (Patent Document 2) discloses a spherical phenol resin hardened substance obtained by reacting phenol and formaldehyde with an alkaline catalyst in the presence of a suspending agent and thereafter performing hardening reaction with an acidic catalyst. However, the average particle diameter specifically described in Example is 100 to 800 μm.
Japanese Patent Laying-Open No. 50-98537 (Patent Document 3) describes a technique of obtaining a non-thermofusible phenol resin powder by adding a cellulosic compound to an initial condensate obtained by reacting a phenolic compound and a formaldehyde in the presence of at least one of an acidic catalyst and a basic catalyst and a nitrogen-containing compound, granulating the mixture by further continuing the reaction and thereafter performing dehydration/drying. However, the average particle diameter of this phenol resin powder is about 700 μm. Further, the phenol resin powder contains about 6000 ppm of free phenol, and there is room for improvement in view of safety.
Japanese Patent Laying-Open No. 2001-114852 (Patent Document 4) describes a technique of obtaining a spherical phenol resin by condensing a phenolic compound and an aldehyde in the presence of a condensation catalyst and an emulsion dispersant under conditions of a temperature of at least 105° C. and not more than 200° C. and a pressure of at least 1.3 kg/cm2 and not more than 15 kg/cm2. This spherical phenol resin has an average particle diameter of 2 to about 200 μm, as described in Example. However, the technique is accompanied with such complicatedness that the reaction is performed with an autoclave, and there has been such a problem that the particle diameter remarkably fluctuates depending on a stirring method or a rate of stirring. Further, the reaction pattern is essentially similar to that in the aforementioned Patent Document 3, and the chemical structure of the obtained phenol resin is also conceivably equivalent, and hence the phenol resin conceivably contains a large quantity of free phenol.
Japanese Patent Laying-Open No. 59-6208 (Patent Document 5) describes a spherical phenol resin obtained by hardening a dispersion of a resol-type spherical phenol resin, obtained by reacting a phenolic compound and a formaldehyde with a nitrogen-containing compound catalyst in the presence of a water-soluble polymer compound, with an acidic catalyst. However, the spherical phenol resin obtained by this method has a large average particle diameter of about 350 to 520 μm.
Japanese Patent Laying-Open No. 2002-226534 (Patent Document 6) discloses a method for producing spherical resin particulates from resorcin and an aldehyde by setting the ratio (weight ratio) of the resorcin and water to 1:5 to 1:100 and adjusting the pH of the reaction system to 5 to 7. These spherical resin particulates have an average particle diameter of 500 nm to 2 μm, as described in Example. However, there is such a problem that only the resorcin can be used as the phenol source, and hence the residual carbon ratio of the obtained phenol resin is conceivably low as compared with a case of employing another phenolic compound such as phenol.
Japanese Patent Laying-Open No. 10-338728 (Patent Document 7) describes a method for producing a spherical phenol resin hardened substance by removing a solvent from a homogeneous mixed liquid containing a phenol resin, a cellulose derivative and the solvent, causing phase separation of the phenol resin and the cellulose derivative, hardening the phenol resin and thereafter removing the cellulose derivative from the composite of the phenol resin hardened substance and the cellulose derivative. A spherical phenol resin hardened substance having an average particle diameter of 28 nm to 5 μm is obtained by this method. However, an organic solvent problematic to the environment and safety of the human body must be used in this method. Further, the phase separation reaction in a solid phase is utilized, and hence a long time of 21 hours to 114 hours is required for formation/extraction of the particles. Japanese Patent Laying-Open No. 7-18043 (Patent Document 8) discloses a method for producing a spherical phenol-formaldehyde-based resin by reacting a phenol compound and formaldehyde in a specific quantity of water or a mixed solvent of water/water-compatible organic solvent in the presence of an acidic catalyst while condensing the solvent and hardening deposited novolac spherical particles by reaction with a hardening agent. According to this method, a spherical phenol resin having a particle diameter of about 9 μm or 15 μm can be obtained, for example. However, it cannot be said that the spherical phenol resin obtained by this method is sufficiently satisfactory in the point of the particle size distribution. Further, the reaction pattern is essentially similar to that in the aforementioned Patent Document 3, and the chemical structure of the obtained phenol resin is also conceivably equivalent, and hence the phenol resin conceivably contains a large quantity of free phenol.
Although various methods such as that employing an additive such as a suspending agent or an emulsion dispersant and that optimizing polymerization conditions etc. for the phenol resin have generally been proposed as techniques for obtaining particulates of phenol resins, phenol resin particles having a minute average particle diameter of not more than 20 μm, preferably not more than 10 μm, hardly containing secondary aggregates, having an extremely small content of a monomer phenolic compound and having high safety and a method for producing the same have not been proposed. Further, such a phenol resin powder that the shapes of the particles thereof are spherical and the particle size distribution of the particles is sufficiently narrow in addition to these characteristics and a method for producing the same are not proposed.
For example, even if the polymerization conditions etc. for the phenol resin are optimized, it follows that the obtained phenol resin contains a monomer phenolic compound in a high content substantially identically to the prior art when the polymerization conditions for polymerizing the phenolic compound and the aldehyde themselves are essentially equivalent to the polymerization conditions having been employed in general. In such a method for producing a phenol resin powder that a rate of stirring influences the particle size, the particle size distribution inevitably widens since the inner portion of a reaction vessel cannot be continuously homogeneously stirred.
An integrated circuit device such as an IC (Integrated Circuit) or a memory generally consists of a semiconductor element, an insulating support substrate, a lead frame and a lead, and a sealing material or an adhesive is employed for sealing and bonding these. In general, it has been a mainstream tendency to employ a resin composition containing an inorganic filler such as spherical silica, epoxy resin and a hardening agent for such a sealing material or an adhesive.
In recent years, however, heat resistance has been required to a sealing material and an adhesive, in order to cope with increase of a soldering temperature resulting from transition to lead-free solder and application to an electronic component such as an on-vehicle electronic component requiring a high-temperature operation assurance. Further, while refinement of the filler in the sealing material and the adhesive and reduction in viscosity of the sealing material and the adhesive are required in order to cope with further refinement of internal wires of the integrated circuit chip, it has been difficult to satisfy these both new required characteristics with conventional blending.
In other words, epoxy resin which is an organic substance and spherical silica (fused silica) which is an inorganic substance are remarkably different in linear expansion coefficient from each other, and hence such deterioration comes into question that stress is formed on the interface between the epoxy resin and the spherical silica to cause cracks in production through a soldering step or the like or following temperature rise/temperature reduction in use.
Japanese Patent Laying-Open No. 11-172077 (Patent Document 9) describes a technique of blending an amino-based silane coupling agent acting on a silica surface to a composition for sealing a semiconductor in order to improve mechanical characteristics of a hardened substance. However, heat resistance of the silane coupling agent itself is low, and hence heat resistance of the sealing material is also relatively low depending on the heat resistance of the silane coupling agent.
As a means for canceling stress formation on the interface between the aforementioned epoxy resin and the spherical silica, an organic filler which is an organic substance may conceivably be employed in place of the inorganic filler such as the spherical silica. This is because the difference between the linear expansion coefficients of the filler and the epoxy resin is reduced due to the employment of the organic filler. For example, Japanese Patent Laying-Open No. 2000-269247 (Patent Document 10), Japanese Patent Laying-Open No. 2002-226824 (Patent Document 11) and Japanese Patent Laying-Open No. 2004-168848 (Patent Document 12) describe that an organic filler can be employed for a sealing material for a semiconductor or an adhesive for a semiconductor. However, there is no proposal as to a specific organic filler having the aforementioned required characteristics.
The phenol resin is a material excellent in heat resistance, dynamical performance and electric characteristics, and utilized as various industrial materials such as that for an electronic material. If a hardened substance of the phenol resin can be employed as an organic filler, the excellent characteristics belonging to this phenol resin can be supplied to the sealing material or the adhesive for a semiconductor.
However, there has heretofore been proposed no phenol resin hardened substance having high heat resistance and implementing refinement of resin particles and reduction in viscosity in a case of forming a sealing material or an adhesive. Further, while it is desired that an ionic impurity content, particularly a halogen ion content is small as the organic filler employed for the sealing material for a semiconductor or the adhesive for a semiconductor, the phenol resin is in the first place ordinarily polymerized in an aqueous medium with an ionic catalyst, and hence it has been difficult to obtain such a phenol resin hardened substance that the ionic impurity content is reduced to a degree applicable to a semiconductor use.
Japanese Patent Laying-Open No. 10-60068 (Patent Document 13) and Japanese Patent Laying-Open No. 2-245011 (Patent Document 14) describe phenol resins in which the contents of ionic impurities are reduced by specific washing treatments, and mention that these phenol resins are useful for application to sealing materials for semiconductors or the like. However, the phenol resins described in these documents are unhardened, and not employed as organic fillers. Further, the washing methods described in these documents cannot be employed for removal of an ionic impurity from a phenol resin hardened substance.    Patent Document 1: Japanese Patent Laying-Open No. 57-177011    Patent Document 2: Japanese Patent Laying-Open No. 2000-239335    Patent Document 3: Japanese Patent Laying-Open No. 50-98537    Patent Document 4: Japanese Patent Laying-Open No. 2001-114852    Patent Document 5: Japanese Patent Laying-Open No. 59-6208    Patent Document 6: Japanese Patent Laying-Open No. 2002-226534    Patent Document 7: Japanese Patent Laying-Open No. 10-338728    Patent Document 8: Japanese Patent Laying-Open No. 7-18043    Patent Document 9: Japanese Patent Laying-Open No. 11-172077    Patent Document 10: Japanese Patent Laying-Open No. 2000-269247    Patent Document 11: Japanese Patent Laying-Open No. 2002-226824    Patent Document 12: Japanese Patent Laying-Open No. 2004-168848    Patent Document 13: Japanese Patent Laying-Open No. 10-60068    Patent Document 14: Japanese Patent Laying-Open No. 2-245011